On Sun, Nov 13, 2016 at 03:37:18PM +0100, Rafael J. Wysocki wrote:
Hold on a sec. I thought during LPC someone (Peter?) made a point that when RT thread run, we should bump the frequency to max? So, schedutil is going to trigger schedutil to bump up the frequency to max, right?
No, it isn't, or at least that is unlikely.
sugov_update_commit() sets sg_policy->work_in_progress before queuing the IRQ work and it is not cleared until the frequency changes in sugov_work().
OTOH, sugov_should_update_freq() checks sg_policy->work_in_progress upfront and returns false when it is set, so the governor won't see its own worker threads run, unless I'm overlooking something highly non-obvious.
FWIW my intention with the original version of this patch (which I neglected to communicate to Viresh) was that it would depend on changing the frequency policy for RT. I had been using rt_avg. It sounds like during LPC there were talks of using another metric.
It does appear things would work okay without that but it also seems a bit fragile. There's the window between when the work_in_progress gets cleared and the RT kthread yields. I have not thought through the various scenarios there, what is possible and tested to see if it is significant enough to impact power-sensitive platforms.
thanks, Steve